Pigs frequently are used in cleaning pipelines or separating product batches in a pipeline. In pipelines having internal obstructions, or substantially varying diameter, there is significant risk in using a pig which may become stuck, and such risk is enormous in deepwater pipelines where the cost in lost time in recovering a stuck pig and reopening the pipeline are substantial. For such pipelines, it is attractive to use a foam pig which is capable of changing size to get around obstructions or adapt to a different pipe diameter. However, foam pigs are not without problems also, and have been known to occasionally fail. Accordingly, discrete solids such as sand or rust may build up a solid bed of sufficient thickness in front of the pig so as to cause the pig to partially collapse and ride over it. Paraffinic or asphaltic solids may build up a column in front of the pig of sufficient length so as to stop forward motion due to the column's high yield stress and effective viscosity.
Accordingly, the present invention is directed to overcoming the above-identified problems of the art by providing a novel pipeline pig which not only solves the above problems but also has other advantages as will become apparent hereinafter.